The Tor Browser: comparison xpcom/glue/nsProxyRelease.h

--1:000000000000
+:5060c778c91a
+/* -*- Mode: C++; tab-width: 3; indent-tabs-mode: nil; c-basic-offset: 3 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+* License, v. 2.0. If a copy of the MPL was not distributed with this
+* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef nsProxyRelease_h__
+#define nsProxyRelease_h__
+#include "nsIEventTarget.h"
+#include "nsIThread.h"
+#include "nsCOMPtr.h"
+#include "nsAutoPtr.h"
+#include "MainThreadUtils.h"
+#include "mozilla/Likely.h"
+#ifdef XPCOM_GLUE_AVOID_NSPR
+#error NS_ProxyRelease implementation depends on NSPR.
+#endif
+/**
+* Ensure that a nsCOMPtr is released on the target thread.
+*
+* @see NS_ProxyRelease(nsIEventTarget*, nsISupports*, bool)
+*/
+template <class T>
+inline NS_HIDDEN_(nsresult)
+NS_ProxyRelease
+(nsIEventTarget *target, nsCOMPtr<T> &doomed, bool alwaysProxy=false)
+{
+T* raw = nullptr;
+doomed.swap(raw);
+return NS_ProxyRelease(target, raw, alwaysProxy);
+}
+/**
+* Ensure that a nsRefPtr is released on the target thread.
+*
+* @see NS_ProxyRelease(nsIEventTarget*, nsISupports*, bool)
+*/
+template <class T>
+inline NS_HIDDEN_(nsresult)
+NS_ProxyRelease
+(nsIEventTarget *target, nsRefPtr<T> &doomed, bool alwaysProxy=false)
+{
+T* raw = nullptr;
+doomed.swap(raw);
+return NS_ProxyRelease(target, raw, alwaysProxy);
+}
+/**
+* Ensures that the delete of a nsISupports object occurs on the target thread.
+*
+* @param target
+*        the target thread where the doomed object should be released.
+* @param doomed
+*        the doomed object; the object to be released on the target thread.
+* @param alwaysProxy
+*        normally, if NS_ProxyRelease is called on the target thread, then the
+*        doomed object will released directly.  however, if this parameter is
+*        true, then an event will always be posted to the target thread for
+*        asynchronous release.
+*/
+NS_COM_GLUE nsresult
+NS_ProxyRelease
+(nsIEventTarget *target, nsISupports *doomed, bool alwaysProxy=false);
+/**
+* Class to safely handle main-thread-only pointers off the main thread.
+*
+* Classes like XPCWrappedJS are main-thread-only, which means that it is
+* forbidden to call methods on instances of these classes off the main thread.
+* For various reasons (see bug 771074), this restriction recently began to
+* apply to AddRef/Release as well.
+*
+* This presents a problem for consumers that wish to hold a callback alive
+* on non-main-thread code. A common example of this is the proxy callback
+* pattern, where non-main-thread code holds a strong-reference to the callback
+* object, and dispatches new Runnables (also with a strong reference) to the
+* main thread in order to execute the callback. This involves several AddRef
+* and Release calls on the other thread, which is (now) verboten.
+*
+* The basic idea of this class is to introduce a layer of indirection.
+* nsMainThreadPtrHolder is a threadsafe reference-counted class that internally
+* maintains one strong reference to the main-thread-only object. It must be
+* instantiated on the main thread (so that the AddRef of the underlying object
+* happens on the main thread), but consumers may subsequently pass references
+* to the holder anywhere they please. These references are meant to be opaque
+* when accessed off-main-thread (assertions enforce this).
+*
+* The semantics of nsRefPtr<nsMainThreadPtrHolder<T> > would be cumbersome, so
+* we also introduce nsMainThreadPtrHandle<T>, which is conceptually identical
+* to the above (though it includes various convenience methods). The basic
+* pattern is as follows.
+*
+* // On the main thread:
+* nsCOMPtr<nsIFooCallback> callback = ...;
+* nsMainThreadPtrHandle<nsIFooCallback> callbackHandle =
+*   new nsMainThreadPtrHolder<nsIFooCallback>(callback);
+* // Pass callbackHandle to structs/classes that might be accessed on other
+* // threads.
+*
+* All structs and classes that might be accessed on other threads should store
+* an nsMainThreadPtrHandle<T> rather than an nsCOMPtr<T>.
+*/
+template<class T>
+class nsMainThreadPtrHolder MOZ_FINAL
+{
+public:
+// We can only acquire a pointer on the main thread. We to fail fast for
+// threading bugs, so by default we assert if our pointer is used or acquired
+// off-main-thread. But some consumers need to use the same pointer for
+// multiple classes, some of which are main-thread-only and some of which
+// aren't. So we allow them to explicitly disable this strict checking.
+nsMainThreadPtrHolder(T* ptr, bool strict = true) : mRawPtr(nullptr), mStrict(strict) {
+// We can only AddRef our pointer on the main thread, which means that the
+// holder must be constructed on the main thread.
+MOZ_ASSERT(!mStrict || NS_IsMainThread());
+NS_IF_ADDREF(mRawPtr = ptr);
+}
+// We can be released on any thread.
+~nsMainThreadPtrHolder() {
+if (NS_IsMainThread()) {
+NS_IF_RELEASE(mRawPtr);
+} else if (mRawPtr) {
+nsCOMPtr<nsIThread> mainThread;
+NS_GetMainThread(getter_AddRefs(mainThread));
+if (!mainThread) {
+NS_WARNING("Couldn't get main thread! Leaking pointer.");
+return;
+}
+NS_ProxyRelease(mainThread, mRawPtr);
+}
+}
+T* get() {
+// Nobody should be touching the raw pointer off-main-thread.
+if (mStrict && MOZ_UNLIKELY(!NS_IsMainThread())) {
+NS_ERROR("Can't dereference nsMainThreadPtrHolder off main thread");
+MOZ_CRASH();
+}
+return mRawPtr;
+}
+bool operator==(const nsMainThreadPtrHolder<T>& aOther) const { return mRawPtr == aOther.mRawPtr; }
+NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsMainThreadPtrHolder<T>)
+private:
+// Our wrapped pointer.
+T* mRawPtr;
+// Whether to strictly enforce thread invariants in this class.
+bool mStrict;
+// Copy constructor and operator= not implemented. Once constructed, the
+// holder is immutable.
+T& operator=(nsMainThreadPtrHolder& other);
+nsMainThreadPtrHolder(const nsMainThreadPtrHolder& other);
+};
+template<class T>
+class nsMainThreadPtrHandle
+{
+nsRefPtr<nsMainThreadPtrHolder<T> > mPtr;
+public:
+nsMainThreadPtrHandle() : mPtr(nullptr) {}
+nsMainThreadPtrHandle(nsMainThreadPtrHolder<T> *aHolder) : mPtr(aHolder) {}
+nsMainThreadPtrHandle(const nsMainThreadPtrHandle& aOther) : mPtr(aOther.mPtr) {}
+nsMainThreadPtrHandle& operator=(const nsMainThreadPtrHandle& aOther) {
+mPtr = aOther.mPtr;
+return *this;
+}
+// These all call through to nsMainThreadPtrHolder, and thus implicitly
+// assert that we're on the main thread. Off-main-thread consumers must treat
+// these handles as opaque.
+T* get()
+{
+if (mPtr) {
+return mPtr.get()->get();
+}
+return nullptr;
+}
+const T* get() const
+{
+if (mPtr) {
+return mPtr.get()->get();
+}
+return nullptr;
+}
+operator T*() { return get(); }
+T* operator->() { return get(); }
+// These are safe to call on other threads with appropriate external locking.
+bool operator==(const nsMainThreadPtrHandle<T>& aOther) const {
+if (!mPtr || !aOther.mPtr)
+return mPtr == aOther.mPtr;
+return *mPtr == *aOther.mPtr;
+}
+bool operator!() { return !mPtr; }
+};
+#endif

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comparison: xpcom/glue/nsProxyRelease.h

xpcom/glue/nsProxyRelease.h